The present disclosure relates to an image forming apparatus including a heating portion configured to raise the temperature of a heating roller, and relates to a fixing operation control method applied to the image forming apparatus.
An image forming apparatus using an electrophotographic method includes a fixing device for fixing on a print sheet a toner image transferred onto the print sheet. The fixing device includes: a heating device such as a heater; a heating roller (a rotating member), the surface of which is heated by the heating device; and a pressure roller which is brought into pressure contact with and driven by the heating roller. The heating roller is rotatably supported by the fixing device and is driven to rotate by a driving force transmitted to the heating roller. When a print sheet has been conveyed to a nip portion formed between the heating roller and the pressure roller, then during the conveyance of the print sheet by the heating roller and the pressure roller, a toner image on the print sheet is fused by the heat of the heating roller and fixed on the print sheet by the pressurization of the pressure roller. Further, in the fixing device, a temperature sensor detects the surface temperature of the heating roller, and based on the detection result, the heating of the heating device is controlled so that the temperature in the nip portion is a fixing temperature, which enables the fixing of toner.
Conventionally, this kind of fixing device includes a power saving function for reducing the power consumed when the heating device performs heating. The conventional power saving function stops the heating of the heating device until the input of a print job. Then, when a print job has been input, the conventional power saving function starts the heating of the heating device and controls the temperature of the heating roller to rise to the fixing temperature. Then, while a fixing process is being performed at the fixing temperature, the power saving function performs constant temperature control to maintain the temperature of the heating roller at the fixing temperature. Further, when the print job has been completed, the power saving function stops the heating of the heating device, or performs standby temperature control for maintaining the temperature of the heating roller at a temperature lower than the fixing temperature.
It should be noted that a fixing device or an image forming apparatus including various power saving functions is known as the conventional art. For example, an apparatus capable of selecting between an ecology-oriented mode and a printing-time-oriented mode is known. An apparatus capable of setting a plurality of modes such as a normal mode and an energy-saving mode is known. Further, an apparatus that changes a fixing speed in accordance with the number of print sheets to pass through a fixing device is known.